Part II:

I think using a torsion lift for tire clearance is a bad idea......the key here is that I "think". Lots and lots of guys do this and have success in their eyes.

Going further with my above explanation, when you lift with torsion bars you are simply moving your RESTING ride height. Your bump stops and droop stops are still in the same location. We might have gained a little droop travel with our shock extensions or cognito upper arms but we are still stuck with about 6-7" of travel. So our brand new 285's now clear when we turn the wheel, the problem is that we are clearing these tires above the centerline of the wheel meaning that if we compress the suspension the tire is going to hit.....big time. At stock ride height the interference point on the fender is just slightly above the centerline of the wheel, once lifted 2" you now have about 1/2" to 3/4" of clearance (remember the tire is round). In my mind this will only work for tire clearance in the driveway or in the Walfart parking lot. If you compress the suspension while turning sharp you will compress the suspension up to the center line of the wheel and then some maybe even 3" further. So now your 1/2" of clearance just turned into 1/2" of bent plastic.

To summarize, in my mind, the idea is to clear what ever tire you have at full compression or close to it. If the tire won't clear when it's shoved into the fender then you have problems....you just may not know it untill it's too late.

 

Part II:

I think using a torsion lift for tire clearance is a bad idea......the key here is that I "think". Lots and lots of guys do this and have success in their eyes.

Going further with my above explanation, when you lift with torsion bars you are simply moving your RESTING ride height. Your bump stops and droop stops are still in the same location. We might have gained a little droop travel with our shock extensions or cognito upper arms but we are still stuck with about 6-7" of travel. So our brand new 285's now clear when we turn the wheel, the problem is that we are clearing these tires above the centerline of the wheel meaning that if we compress the suspension the tire is going to hit.....big time. At stock ride height the interference point on the fender is just slightly above the centerline of the wheel, once lifted 2" you now have about 1/2" to 3/4" of clearance (remember the tire is round). In my mind this will only work for tire clearance in the driveway or in the Walfart parking lot. If you compress the suspension while turning sharp you will compress the suspension up to the center line of the wheel and then some maybe even 3" further. So now your 1/2" of clearance just turned into 1/2" of bent plastic.

To summarize, in my mind, the idea is to clear what ever tire you have at full compression or close to it. If the tire won't clear when it's shoved into the fender then you have problems....you just may not know it untill it's too late.

This is a great thread.

Where will it hit? With space aplenty in the upper fender I'm confused.

Also, what have you guys used to back your fender liners on 08 models?

 

So then why does my truck ride so bad after I cranked my bars?









































JUST KIDDING. Nicely stated info.

 

thats some good info and a mouthful..its a wonder why we do the things we do..lol thanks for the info and the write up.

 

has anyone taken out the bumpstops???

 

I'm debating on at least going to a much shorter one, but the downside is that in reality GM tuned this suspension to use them to help stiffen up the spring rate. Hell GM has them touching at stock ride height. I'm afraid the crash into the shorter stiffer (poly maybe) bump stop might be too much. Then again the extra 1" or 2" worth of travel might let the shocks do their job of dampening chassis movement.....that is if the shocks have that much travel in compression. I've got a lot of questions on the subject.

 

Which leads to the wrong assumption that tighting the torsion bar adjusting bolt actually "tightens" the torsion bars and makes them stiffer. This is just wrong....wrong....wrong. Of course I can jump up and down untill I'm blue in the face, but that won't make you believe me. On to the theory.

The first thing you have to undertsand is that torsion bars are just coil springs that are straitened out and are twisted instead of bent. So they act just the same. Lets use a coil spring in our example and then bridge the gap to our torsion bars. Lets say we have a 500 lb/in spring and we put it on a car that has 1000 lb per corner. Assuming that the spring is in line with the wheel for simplicities sake we will have to compress that spring 2" for the chassis to settle out. 1000 lb's = 1000 lb's. Lets say you want to lift the vehicle 1", so you add a 1" spacer on top of the spring. The spring is not going to compress any more than it already is because you have added no more weight, you've simply changed the installed height of the spring.

Now lets jump over to torsion bars, the twisting motion on the bar is exactly the same as the compression of a coil spring. You are bending a spring only in different directions. By twisting the torsion bar with the adjusting bolt you are simply changing the preload on the spring, not adding any more weight. So when we "crank" on our torsion bars we are not adding any more weight or twisting the bar any more than stock.....we are simply changing the installed "height" of the spring.

I think you must consider the fact that since we've changed the normal ride height of the truck by cranking up the bars, the TB's will be subjected to further stress ( compression, as in your example).

Since you've removed some of the sag portion of the travel, you will now have to push the TB's farther to get full travel. Since they have a rising rate of resistance, they WILL be "tighter" in the later part of the travel.

Clear as mud?

 

made a crude chart to help me with my point.

 

I dont really like reading much, so If Nick says so, thats good enough for me. LOL. Weather some agree with him or not, I do, and I believe when it comes to lifts he knows his ****.

 

In the link in the first post, I couldn't see any statement about cranking the TB's' affect on ride and whether or not it "stiffens" the ride. I agree with Nick's post, but not with LMM_GUY's.

 

Great this is exactly the point I wanted to discuss.

Edit: I changed my response because I missed the point that 450zzz was making.

450zzz,

Initially I was making the argument about there being additional tension at your resting ride height.You are absolutely right we will be technically twisting the torsion bar further when we BOTTOM out the the suspension. Will this hurt the torsion bars? I think not, the amount you have to bend spring steel to permanently deform it is unreal. I personally don't think the extra 5 maybe 10 degrees of rotation will ever hurt the bars. The very few guys that have had their bars "wear out" had very high mileage trucks. I think it may be easier on the truck in general because the torsion bars will help slow the chassis down before bottoming out instead of soley relying on the bump stops and shocks to dampen that last few inches of travel.

I think we need to start putting some real numbers into this discussion. I have the ability to dig out the formula's to actually calculate when steel will deform. We can put some real world numbers to this discussion. First we need to find the torsion bar rates, I remember a thread on the subject.

 

Great this is exactly the point I wanted to discuss.

Edit: I changed my response because I missed the point that 450zzz was making.

450zzz,

Initially I was making the argument about there being additional tension at your resting ride height.You are absolutely right we will be technically twisting the torsion bar further when we BOTTOM out the the suspension. Will this hurt the torsion bars? I think not, the amount you have to bend spring steel to permanently deform it is unreal. I personally don't think the extra 5 maybe 10 degrees of rotation will ever hurt the bars. The very few guys that have had their bars "wear out" had very high mileage trucks. I think it may be easier on the truck in general because the torsion bars will help slow the chassis down before bottoming out instead of soley relying on the bump stops and shocks to dampen that last few inches of travel.

I think we need to start putting some real numbers into this discussion. I have the ability to dig out the formula's to actually calculate when steel will deform. We can put some real world numbers to this discussion. First we need to find the torsion bar rates, I remember a thread on the subject.

Nice original post and very thorough. However I would have to side with 450zzz. I would think that preloading the bars alone is affecting (stiffening) the ride. I don’t think he was talking so much about deforming the bars, but just disagreeing with you stating that cranking alone has no affect.

 

Subscribing to get in on the "putting it to number discusssion".

 

I'm going to watch this, I have "green" keys and my truck rides really stiff.

 

I think that tightening TB's increases the spring rate to lift it higher in the air like 450zzz said in addition to that the shorter amount of suspension travel just adds to the rough ride.

I added coil spacers to my old 05 4runner and I swear it rode rougher.

 

It definately doesn't change the spring rate, it does change the preload on the springs. A higher preload will feel stiffer.

 

If the t-bars are not up against the bump stops, you are not pre-loading them. If you look at a coil over from a dirt bike, it has a fixed length.Therefore you can preload that type of suspension. By simply "raisng" your t-bars does not preload them, unless you crank them beyond there amount of travel. Does installing a lift block under a leaf spring preload it? I think not.

 

I'm do not agree with you. If you crank the back of the torsion bar in relationship to the front, your are "pre-loading" that bar. It is the same if you had a coil-spring and compressed it some at install so the spring is pre-loaded when the vehicle is at rest.

 

The ride is the lest of my worries I don't want the add strain on the CV.

Back in the day some guys where cutting down there bump stop to a more triangleler shape. Others also put smaller ones on might search out those members and as them how it went.

 

Tightening the torsion bars is not the same as putting a spacer in a coil spring. Even if the spring rate is linear, you are still further along in the linear relationship.

I think the question is: Is the change in "pre-load" noticeable or is the main factor the suspension running out of travel? or both?

 

Think of it this way. By raising the resting ride height, the lower control arms angle down further than stock. However, this alone does not increase spring rate. What does, causing the "harsher" ride, is when the suspension compresses. Since there is now more room for upward travel, the bars twist farther than they did at the stock height. The farther they twist, the stiffer the spring rate becomes (in theory). I don't have the time right now - maybe later - but a diagram would really help with what I'm trying to say. LMM Guy - the torsion and coil comparison has one flaw, being that eventually coils compress to the point that all of the coils come into contact and they can no longer compress (extreme compression situations where no other factors such as bumpstops come into play) whereas the only limiting factor in how much a torsion bar can "compress" are other suspension components, ie bump stops, fenders, etc. or until the metal deforms. However for all intensive purposes your comparison helps put into laymans terms what is usually considered "PhD" material to most.

 

great write up I totally agree no need to crank t bars. Just get a leveling kit or a mild lift and forget it.

 

A leveling kit will be the same as cranking the t-bars.

 

Our torsion bars are NOT progressive rate... they are linear. It is very hard to make a torsion bar that is progressive, to do so you have to tapper the bar. Ours are strait....so the rate is strait. You'll add XXX lb's of force for every degree it's twisted.

You will not increase the resulting force or the rate of a spring by putting a spacer on the end. You will increase the rate if you put a spacer between the coils....which is not what I'm talking about. Coil springs do have the downfall of being able to stack coils effectively giving up the ability to be a spring. Torsion bars or leaf springs will not do this, you can bend them untill you go outside of their yeild point then they stay bent.

Lets simplify this further......take a spring with a rate of 10 lb/in, put a 20 lb weight on top of the spring and it is going to compress 2" You agree? Now put a 1" spacer that weights nothing between the weight and the spring.......will that spring compress any?

Pre-load: Lets better explain what is going on here. Say we take a 10" coil spring with a rate of 100 lb/in and compress it 2" to fit on our shock. We will effectively have 200 lb of "pre-load" on the spring. Then we crank down the spring seat another 1" and end up with 300 lb's of pre-load. Now lets take this shock and put it on a bike that will put 400 lb's of force on it. The bike will compress the shock 1"......it will take 300 lb's to overcome the preload then there should be 100 lb's left to compress the shock. You could adjust the spring seat down another inch and the bike would set 1" higher, but the force of the spring would be the same, it won't change untill you either add more weight or run out of travel.

To relate this to our trucks, we already have met the equilibreum point when we set the truck on the ground. All we are doing is changing the installed "height" of the spring. By cranking down the spring collar on our coil over or our bolts on our torsion bar all you are doing is changing the height of the point of which the spring acts on the chassis. The spring will not compress any more untill you bottom out the upper arm on the stop.

P.S. I'll have more time to dig up our actuall spring rates and find my torsion calculations later tonight.

 

To relate this to our trucks, we already have met the equilibreum point when we set the truck on the ground.

I see what your saying, with this information, I retract my statement that by cranking the bars we are "pre-loading" them further than if we don't. I hadn't considered the fact that the truck is twisting them addtionally as it sits at rest on it's wheels. Assuming the additional crank at the keys is less than the final amount of twist when at rest, we have not changed the pre-load at all. Good info here...

 

LMM_Guy is pretty much right.

The "pre-load" on our torsion bars is the weight of the vehicle. And that's it. It doesn't matter if you rotate them 5 degrees or 10 degrees or turn them a whole "notch" with the same spring height, the "pre-load" is the static load placed on the spring regardless of ride height of the vehicle. Think about it from the torsion bar's perspective: it doesn't know if it's on a stock height truck or modified height or lifted, or green or brown or purple keys, or on a Ford or a Dodge or a HMMV or a Nissan. It just knows about load. And it's being asked to hold X lbs of load off a lever (the A-arm) and given its diameter, it twists Y degrees. It's no more complicated than that. If you disagree with this idea, I suggest reading a book like "Chassis Engineering", by Herb Adams. It's a well written book with good example, equations, and diagrams.

The way to change the pre-load is to change the amount of load on them. That can be done a few ways such as by transferring load to another item (like the spring jouncers that look like the bump stops). Or by adding a heavy front bumper - that will increase the preload. Or (effectively) by changing the geometries in the front A-arm suspension design.

I, too, believe that we are not going to introduce spring fatigue by raising the pre-load height of the vehicle, then repeatedly forcing them to the original compressed height defined by the jouncer.

The concerns about accelerated wear on certain parts like CV joints and tie rod ends and ball joints are warranted. The amount of load on these parts goes up exponentially, something like the chart presented earlier.

Another concern is handling - by changing the static angles on the A-arms we have introduced changes in how the vehicle will handle - things like anti-squat, anti-roll and a simple alignment cannot correct for these items. I believe we are putting more load on our anti-sway bar by turning up our keys, but again not enough to be concerned. Now, I have raised my LMM's front profile by 1.5 inches. To compensate (not correct) for these handling concerns, I'll be also putting a slight spacer between the jouncer and its mount to correct for that to make it more-like-stock again. The jouncer does play an important part in the vehicle's handling, and I believe that correcting for it after lifting with green keys is an often overlooked item.

On my LB7, we swapped to green keys. On my LMM, we simply re-adjusted the stock keys. The effects are the same, and thus were the results. I believe that Nick has also correctly identified a primary issue with turning the keys too far - limiting suspension droop.

'nuff for now, this post is long enough.

--Rob

 

Another concern is handling - by changing the static angles on the A-arms we have introduced changes in how the vehicle will handle - things like anti-squat, anti-roll and a simple alignment cannot correct for these items. I believe we are putting more load on our anti-sway bar by turning up our keys, but again not enough to be concerned. Now, I have raised my LMM's front profile by 1.5 inches. To compensate (not correct) for these handling concerns, I'll be also putting a slight spacer between the jouncer and its mount to correct for that to make it more-like-stock again. The jouncer does play an important part in the vehicle's handling, and I believe that correcting for it after lifting with green keys is an often overlooked item.

You're talking about putting a spacer underneath the yellow compression bumper on the lower A-arm to restore it's relationship to travel when at stock height? My truck actually sat on the jounce stop when stock and rode terrible. I cranked it slightly at first just to lift it off the jounce stop and it rode much better.
My ride now with green keys and Cognito UCA's is as good as it was when slightly cranked (better than stock). Cornering might be reduced but with the wider tires, the stability feels the same.

 

Correct me if I'm wrong but isn't tightening the torsion bars is like twisting a coil spring tighter or compressing it more.

If you tighten the torsion bars more it puts downforce on the A-arm and lifts the truck up more.

 

really in depth info. Hard to understand at first, but it's right. I actually thought it was the other way around, but after reading this, I understand, and it makes perfect sense.

 

Okay, the *just* will be key to a decent ride. Mine stock sat on the jounce bumper too much.

 

Ok the two BIG idea's I've seen come out of these discussions that I would like to dive into more are:

1. The added "twist" for lack of a better term at full compression because of us lifting the truck. I don't think it's enough to matter at all, but I want to prove it with math.

2. The effect that bump stops have on ride, this next to the lack of droop travel is really the key to a good ride......lets discuss further.

 

Good. I like this.

Our torsion bars are NOT progressive rate... they are linear. It is very hard to make a torsion bar that is progressive, to do so you have to tapper the bar. Ours are strait....so the rate is strait. You'll add XXX lb's of force for every degree it's twisted.

False. The opposite is true. The best example is a fishing rod. The end of it is thin, and responds to a small load. The thicker part of the rod only starts to bend under a larger load - hence a progressive rate.

The TB is uniform thickness front to back, therefore it will have an increasing # load necessary for each degree rotation.

I doubt if cranking them up will cause them to fail - like you said earlier, they can take a huge amount of stress before they will permanently deform.


2) I agree 100%. Look at a trophy truck. 2' travel, and they have roughly half of that in sag? Our trucks only have 7" to work with, so when you crank up the TB's you will upset the balance.

My observation when tuning my TB's was this. When the bars were low, I had a rough compression when hitting a bump, and since the suspension was already touching the bumpstops I think it's safe to say that there was so little travel left that I needed to go higher.

I raised them up - guessing 6 turns? and the ride was pretty good. I went two turns higher, and it was harsh again. I think this was the point that I was too close to the top-out stops. I started coming back down 1/2 turn at a time and settled at the point where it felt the best.

As I sit now, on one side the bumpstop is barely touching, and theres about 1/4" clearance on the other side. I know it sounds bad.

Even when I jack the truck up off the ground there's only about 1" of clearance. pic below.

 

Bump stops: are really called jounce bumpers for our trucks. I remember being concerned about this for my LB7. There was also discussion on another diesel board about this some time ago. The dealer told me the suspension is supposed to "rest" on them - i.e. no clearance at normal ride height, like you would see on a normal bump stop. After doing some measuring, I was able to basically confirm this based on info in the factory service manual. They are really like variable-rate springs, and act as a supplement to the regular (torsion bar) spring rate.

So...by raising off of those, you get just the torsion bar spring rate until you contact those bumpers. So you'll have a softer spring rate until you use up that extra travel. If the truck was basically sitting all of its weight on them, then your effective spring rate will then be dictated by the jounce bumper. Based on posts here, I seem to like a firmer ride than others, which is why I want to compensate for that new clearance.

--Rob

 

Bump stops: are really called jounce bumpers for our trucks. I remember being concerned about this for my LB7. There was also discussion on another diesel board about this some time ago. The dealer told me the suspension is supposed to "rest" on them - i.e. no clearance at normal ride height, like you would see on a normal bump stop. After doing some measuring, I was able to basically confirm this based on info in the factory service manual. They are really like variable-rate springs, and act as a supplement to the regular (torsion bar) spring rate.



--Rob

Thanks, I feel better about mine now. See my post above this one.

 

I think it's going to be very difficult (not impossible) to "prove" with math the effect of the spring rate on the ride. There are a lot more variables that come into play. The dampening of the shock, the rotation of the a-arm changes the moment of the force to the ground, and the length/speed of the motion (what size of bump you hit and how fast).

There is a lot going on there besides a slight increase in spring rate. I think it would be relatively easy to calculate the increase in beginning/ending spring force. However the effects of this on the ride would be much more complicated.

For example, you may calculate 1100lbs of force before cranking at rest and 1150lbs after cranking at rest. This doesn't tell us the whole story.....